U.S. patent number 4,187,404 [Application Number 05/926,234] was granted by the patent office on 1980-02-05 for telephone set for optical fibers lines.
This patent grant is currently assigned to Thomson-CSF. Invention is credited to Luigi d'Auria, Pierre Deman.
United States Patent |
4,187,404 |
Deman , et al. |
February 5, 1980 |
Telephone set for optical fibers lines
Abstract
A telephone set for optical fibers lines having a coupler for
directing a first part of the light received from the input optical
fiber on a photo-cell and a second part of this light on a
microphone modulating this second part without electrical
intermediate apparatus, the photo-cell feed alternately a bell or a
receiver, and the light modulated by the microphone is directed via
a dialling system on the output optical fiber.
Inventors: |
Deman; Pierre (Paris,
FR), d'Auria; Luigi (Paris, FR) |
Assignee: |
Thomson-CSF (Paris,
FR)
|
Family
ID: |
9193749 |
Appl.
No.: |
05/926,234 |
Filed: |
July 20, 1978 |
Foreign Application Priority Data
|
|
|
|
|
Jul 25, 1977 [FR] |
|
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77 22757 |
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Current U.S.
Class: |
379/93.01;
379/362; 381/172; 398/42 |
Current CPC
Class: |
H04M
1/003 (20130101); H04B 10/25 (20130101) |
Current International
Class: |
H04B
10/12 (20060101); H04M 1/00 (20060101); H04B
009/00 () |
Field of
Search: |
;179/100,1C,2C,2R
;250/199 ;340/380 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Gruber; Felix D.
Assistant Examiner: Kemeny; E. S.
Attorney, Agent or Firm: Cushman, Darby & Cushman
Claims
What we claim is:
1. A telephone set for receiving from an input optical fiber an
input optical signal and for emitting on an output optical fiber an
output optical signal comprising:
a two-channel coupler for dividing said input optical signal into
first and a second parts;
a photovoltaic cell for converting said first part in an electrical
signal;
a receiver actuated by said electrical signal;
a microphone diaphragm for receiving and directly modulating with
acoustic waves said second part and delivering said output optical
signal.
2. A telephone set according to claim 1, further comprising a bell
system actuated by said electrical signal said bell system
including a capacitor coupled to said electrical signal for storing
charges from said electrical system, a trigger circuit coupled to
said capacitor for periodically discharging said capacitor to
develop a bell-ring signal, and a bell coupled to said bell ring
signal, said telephone set further including first switch for
alternatively connecting said receiver and said bell to said
photo-electric cell.
3. A telephone set according to claim 2 further including a rotary
shutter for periodically interrupting the emission of said output
optical signal; each interruption corresponding to a dialling
pulse.
4. A telephone set according to claim 2 wherein said output optical
signal is emitted onto a plurality of output optical fibers and
siad telephone set further includes a keyboard having a plurality
of channels for simultaneously receiving from said microphone and
propagating said second part of the input optical signal, a
plurality of keys for closing said channels, and means for coupling
said plurality of channels to said plurality of output optical
fibers; each of said keys closing simultaneously at least two
channels for determining a combination of closed channels related
to said key.
5. A telephone set according to claim 2 further comprising means
for partially interrupting the emission of said output optical
signal when said bell is connected to said photo-electric cell; the
level of said emission being reduced to a value allowing to monitor
the continuity of said input and output optical fiber without
demodulating said second part.
6. A telephone set according to claim 2 further comprising a
wide-band output terminal connected to said photo-cell.
7. A telephone set according to claim 2 further comprising
photo-emitting means for delivering onto said output optical fiber
an additional optical signal and a wide-band input terminal
connected to said photo-emitting means.
Description
BACKGROUND OF THE INVENTION
This invention relates to telephones for connecting by optical
fibers a subscriber to a central station. This exchange may be for
example an automatic exchange in the case of a subscriber of the
public network or a tele-data installation for processing simple
numerical data transmitted by means of the dialling unit of the
telephone.
It is known how to produce optical fibers capable of transmitting
modulated luminous signals over relatively long distances with
minimal attenuation. By accepting a band-width which, although
relatively reduced, is nevertheless very much greater than that
(3100 Hz) required for a standard telephone, it is possible to use
fibers of greatly reduced cost enabling a connection of several km
to be established.
However, the telephone line connecting the subscriber's set to the
exchange is also used for transmitting the direct current used for
feeding the set, because regulations prohibit the use of mains
supply and because, it would be unthinkable to return to the system
of the local battery with its limitations attributable to the wear
of cells. In any case, this feed current could not be conducted by
the optical fibers.
SUMMARY OF THE INVENTION
The object of the present invention is to eliminate the need for
any external electrical supply, whether local or remote, in a
telephone for connection by optical fibers by making the telephone
set operate solely on the basis of the luminous energy delivered
thereto by the fibers connecting the telephone set with the
exchange.
To this end, the receiver and the bell are fed from a photovoltaic
cell and a microphone and optomechanical dialling elements are
used.
In accordance with the present invention, there is provided a
telephone set for receiving from an input optical fiber an input
optical signal and for emitting on at least on an output optical
fiber an output optical signal, which comprises:
a two channel coupler for dividing said input optical signal into a
first and a second parts;
a photo-electric cell for converting said first part in an
electrical signal;
a receiver actuated by said electrical signal;
a microphone for first modulating said second part and delivering
said output optical signal.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the invention, and to show how the
same may be carried into effect, reference will be made to the
ensuing description and to the attached figures among which:
FIG. 1 illustrates an optical connection using a telephone set;
FIG. 2 illustrates a diagram of the signals along this
connection;
FIG. 3 illustrates a circuit diagram of a bell set;
FIG. 4 illustrates a circuit diagram of a microphone;
FIGS. 5 and 6 illustrate a rotary dialling switch;
FIG. 7 illustrates a dialling keyboard;
FIG. 8 illustrates a coupling lens for this keyboard;
FIG. 9 illustrates a section through two keys of this keyboard.
DETAILED DESCRIPTION
FIG. 1 shows on the right of a separation axis X.sub.1 X.sub.2 the
essential elements of a telephone set according to the invention
and, on the left of that axis, matching elements situated in the
exchange and connected to the set by the optical fibers FT and FR.
These matching elements are described purely by way of illustration
and their construction may differ considerably according to the
automatic exchange used.
The voice signal to be transmitted to the subscriber arrives on the
line TRON. In an amplifier 102, it is superimposed upon a sawtooth
signal supplied by the generator 101. The corresponding signals 1,
2, and 3 and those described hereinafter are shown in FIG. 2 with,
as reference, a number in a circle which corresponds to the same
reference in FIG. 1. The composite signal issuing from the
amplifier 102 is clipped in a clipper 103 which delivers a
succession of pulses modulated in duration 4. The modulation thus
described is known by the name of PDM. The repetition frequency of
the pulses will be for example 16 kHz in order to avoid any problem
of spectrum overlap.
The output of the amplifier 103 is applied to a light source 104
capable of exciting the optical fiber FT.
It is possible for example to use a semiconductor laser which is a
particularly well-suited device because, on account of the narrow
band width required, the fiber may be large in diameter (several
hundreds of .mu.m) and may correspond without any particular
problem of matching to the emitting surface of such a laser.
The optical fiber FT is connected in the telephone set to a
two-channel coupler 105 which enables the luminous signal to be
divided into two parts for attacking the two outgoing fibers 106
and 107. A coupler of this type is known in the art and may be
produced for example in the form of a variant of the device
described in Applicants copending application Ser. No. 779,094
filed on Mar. 18, 1977 which is incorporated by reference.
The fiber 106 excites a photovoltaic cell 108 which, at its output
terminals, delivers an electrical voltage representing the signal 4
apart from an attenuation factor. A photovoltaic cell of the type
in question may be formed by an ordinary silicon photodiode.
When the hand set is in its rest position, the cell 108 feeds the
bell 109 through the switch 110. The power supplied by an optical
system such as this is inadequate for actuating an ordinary bell
set, so that a device which accumulates the energy and actuates a
bell at regular intervals or any other device adapted to this low
level is used.
When the hand set is lifted, switch 110 is operated by a mechanical
control symbolised by the arrow ER, interrupting the supply of
energy to the bell and connecting the receiver 111 to the terminals
of the cell 108.
The electrical power supplied by the cell 108 is entirely adequate
for actuating this receiver which reproduces the voice signal
transmitted. This is because, as already known, a PDM signal may be
demodulated by being subjected to low-pass filtering, for which
purpose it is possible to use the inertia of the diaphragm of the
receiver which is too great for reproducing the pulses of the
signal 4 and leads to a smoothing of that signal which thus gives
the signal 1. If the receiver in question is too highly rated in
its performance characteristics and renders the sampling noise
audible, a low-pass filter may be introduced between the cell and
the receiver.
The fiber 107 leads to the microphone 112 which is of the
acoustooptical type and enables the luminous signal present in this
fiber to be directly modulated. The sound signal applied to the
microphone is for example like the signal 5. The luminous signal
issuing from the microphone on the optical fiber 113 will thus be
like the signal 6, i.e. a PDM signal comprising an additional
amplitude modulation.
The fiber 113 is connected to the dialling unit 114 which comprises
for example a mechanical dial of ordinary type provided on its
shaft with a rotary optical switch which enables an optical
connection between the fiber 113 and the fiber FR transmitting to
the exchange to be interrupted at regular intervals. It is thus
possible to transmit dialling pulses. The dialling unit 114 also
receives the mechanical control ER which enables the optical switch
to be blocked when the hand set is replaced, thereby interrupting
the connection between, the fibers 113 and FR which guarantees the
privacy of the conversations taking place through the telephone
when the hand set is lifted.
In the exchange, the fiber FR leads to a photoelectric detector
115. This detector comprises a photoelectric cell which enables the
luminous signal transmitted by the fiber FR to be converted into an
electrical signal. This cell may be connected in the usual way with
a polarization because there is no problem of energy supply in the
exchange.
The signal 6 which appears at the output of the detector 116 has to
be demodulated in order to separate the modulation 5 from the
modulation 1 which is always present there. To this end, it is
possible for example to release a monostable circuit 116 with the
leading edge of the pulses of the signal 6. This is because the
position of this edge is constant and bears the amplitude
modulation reproducing the signal 5. For a period which is brief by
comparison with the minimal duration of the pulses, this monostable
circuit opens a sample-and-hold circuit 117 which itself also
receives the signal 6 and memorises the height of the leading edge
of each of the pulses of the signal 6. At its output, this circuit
117 delivers a stepped signal 7 which represents the sampled signal
with a continuous component. For obtaining the signal 5, it is
sufficient to pass this signal 7 through a band-pass filter 118,
for example a standard 300-3400 Hz telephone filter, which
eliminates the continuous component by its low-cut characteristics
and the sampling effect by its high-cut characteristics. The voice
signal 5 is thus obtained at the output connection RON.
In the example of embodiment of the bell set 109 shown in FIG. 3,
the signal delivered by the cell 108 arrives at the input terminals
E.sub.1 and E.sub.2. These terminals are connected to the
low-voltage part of a step-up autotransformer 301. This low-voltage
part is tuned to the repetition frequency of the pulses present at
the input E.sub.1 -E.sub.2 by means of a capacitor 302. This
voltage supplied by the cell 108 thus charged may be of the order
of a few tenths of a volt and the autotransformer 301 enables it to
be converted into a voltage of the order of 10 volts. A diode 303
enables the voltage supplied by the high-voltage part of the
autotransformer to be rectified and a capacitor 304 to be charged.
A circuit consisting of a resistor 305, a capacitor 306 and a
unijunction transistor 307 connected in known manner to operate as
a relaxation oscillator enables the capacitor 304 to be discharged
at regular intervals into a solenoid 308 connected in series with
one of the bases of the transistor 307. The strong current which
then passes into this solenoid projects a magnetised bar 309 onto a
bell 310 which resonates under the impact. A return spring (not
shown) enables the bar 309 to be withdrawn rearwards.
The opto-acoustic microphone shown in FIG. 4 is substantially a
body of revolution about an axis X.sub.3 -X.sub.4 and comprises a
body 401 formed with a cavity closed at its front end by a
diaphragm 402 comprising a flat central surface and a flexible
folded edge facilitating its deflection under the action of the
sound vibrations. The fiber 106 through which the light signals to
be modulated by the sound signal arrives is fixed to the rear of
the body 401 slightly eccentrically relative to the axis X.sub.3
-X.sub.4. It emits a luminous beam which is taken up by a lens 403,
subsequently reflected by the rear polished surface of the
diaphragm 402 and then passes back through the lens 403 by which it
is substantially focussed on the entry face of the fiber 107 which
delivers the luminous signals modulated by the sound vibrations
acting on the diaphragm 403. The fiber 107 is also fixed to the
rear of the body 401 slightly eccentrically relative to the axis
X.sub.3 -X.sub.4. The respective positions of the exit face of the
fiber 106 and the entry face of the fiber 107 are such that the
image of the exit face given by the catadioptric system formed by
the lens 403 and the diaphragm 402 is formed just in front of or
behind the entry face. The reason for this is that, if this image
were to be formed on this entry face itself, any movement of the
diaphragm either forwards or backwards would produce a reduction in
the amount of light transmitted from the fiber 106 to the fiber 107
and the modulation thus produced would correspond to a doubling of
all the sound frequencies to be transmitted. On the other hand, by
shifting the image relative to the entry face, the amount of light
transferred in the rest position is reduced, for example by half,
and the movement in one direction of the diaphragm will tend to
bring the image closer to the entry face by increasing the amount
of light transmitted. Conversely, the movement of the diaphragm in
the other direction will tend to reduce the quantity of light
transmitted. Thus, the modulation will indeed reproduce the sound
signal to be transmitted.
It is known that conventional dials comprise a shaft which rotates
at a constant speed during a number of revolutions determined by
the number of dialling pulses to be transmitted. This shaft drives
a cam which opens a contact set twice per revolution which causes
two pulses to be transmitted for each revolution of the shaft.
One embodiment of the dialling unit 104 consists for example in
fixing to the shaft of a mechanism of the above type a rotating
shutter such as that shown in FIGS. 5 and 6. This shutter consists
of a disc 501 comprising two apertures 502 and 503 in the form of
long sectors of a quarter circle situated diametrically opposite
one another. This disc is fixed at its center to the rotating shaft
504 of the dialling mechanism. A stirrup 601 comprising a slot 602
and two arms 603 and 604 shown in dotted lines in FIG. 5 and in
solid lines in the sectional view of FIG. 6 straddles the disc 501.
The fibers 113 and FR are fixed to the two arms of this stirrup
which they cross from one side to the other, terminating opposite
one another in the slot 602.
A mechanism (not shown) enables the stirrup 601 to be vertically
moved under the effect of the mechanical control ER. In the upper
position, corresponding to FIG. 6, the optical path between the
fibers 113 and FR is blocked by the outer rim of the disc 501. In
the lower position, corresponding to FIG. 5, the luminous signals
can pass between these two fibers, traversing the slot 602 and the
sector 503, the disc 501 being keyed to the shaft 504 in such a way
that, in the rest position of the drive mechanism of this shaft,
the optical path between the fibers 113 and FR passes to the edge
of one of the ends of the sector 501.
Thus, when the hand set is lifted, the stirrup 601 passes from the
upper position to the lower position, establishing communication
with the exchange. On receiving the tone, the operator manipulates
the dial. Under the effect of this manipulation, the disc 501
rotates in the direction of the arrow R and rhythmically interrupts
the optical connection between the fibers 113 and FR which causes a
series of pulses to be received at the exchange, enabling the
exchange to locate the required connection. Since the duration of
these pulses is of the order of several tens of milliseconds under
current standards, they cannot interfer at the exchange with the
modulation pulses 6 (FIG. 2) of which the duration is of the order
of a few tens of microseconds.
When the hand set is replaced, the stirrup 601 returns to its upper
position, breaking the communication.
The state of the line between the telephone set and the exchange
may be monitored by using for the disc 501 a slightly transparent
material which allows a small portion of the luminous energy to
pass through when the stirrup is in its upper position. In that
case, the various levels will be regulated in such a way as to
obtain for example a signal-to-noise ratio of the order of 1 for
the signal 6 at the level of the exchange which completely prevents
the demodulated signal 5 of 6 from being rendered intelligible. On
the other hand, it is known that it is easy, for example by an
autocorrelation technique, to detect pulses having a known
repetition frequency in a high-noise signal so that by detecting
the absence or presence of 4 in 6, it is possible to test the
continuity of the line.
Another embodiment of the disc 501 for ensuring this monitoring
function consists in forming a small hole in the outer rim of the
disc at a point situated between the fibers 113 and FR for the
upper position of the stirrup 601. This hole enables precisely the
quantity of light required for obtaining the desired
signal-to-noise ratio to pass through.
Numerical data may be transmitted by means of a dial, although this
is a fastidious operation. It is much easier to use a dialling
keyboard which also makes it easier to call the number of the
subscriber to be connected.
A keyboard such as this is shown in its standard 16-key form in
FIG. 7. A 12-key version corresponds to the part situated to the
left of the dotted line X.sub.3 -X.sub.4.
This keyboard comprises horizontal channels 701 and vertical
channels 702 intersecting at the locations of the keys 0 to 9 and A
to F. The keys enable these channels to be occulted.
The optical fiber 113 leads to a multiple coupler 703 similar to
the coupler 105 (FIG. 1) and provided with five outgoing fibers
which respectively lead to five emitting lenses 704 which emit the
light emanating from the fiber 103 in certain of the channels 701
and 702.
This light leads to receiving lenses 705 after having passed either
through a single channel or through two channels.
In the latter case, the light issuing from the channel attacked by
an emitting lens is taken up by one of the prisms 706 and
re-emitted in the adjacent channel from which it issues to impinge
on a receiving lens.
These receiving lenses 705 enable the light transmitted to be
injected respectively into the optical fibers FR.sub.1 to FR.sub.5.
Accordingly, these optical fibers transmit in parallel the same
luminous signal as the single fiber FR of FIG. 1. At the exchange,
each of these fibers excites a receiving cell, such as 115, so that
five identical, but separate, electrical signals are obtained. An
adder then enables the signal 6 to be obtained from these five
signals.
By depressing the keys of the keyboard, transmission is interrupted
along certain of the fibers FR.sub.i so that, by separately
processing the five electrical signals induced in the photoelectric
receivers excited by these fibers, it is possible to reconstitute a
dialling signal to the desired standards, for example of the
frequency combination type. A logic device comprising for example a
combination of gates may be used for this purpose. It can clearly
be seen from FIG. 7 that the device shown enables a separate
combination of transmission states of the fibers FR.sub.i to be
obtained for each of the keys of the keyboard. The same result is
also obtained for a keyboard reduced to 12 keys.
The lens shown in FIG. 8 is one example of embodiment both of the
lenses 704 and of the lenses 705.
This lens consists of a block 801 of transparent material, for
example a plastic, which forms a spherical lens. A cavity 802
formed in the flat face of this lens enables it to receive an
optical fiber comprising for example a core 803 and a cladding 804.
This cladding makes it possible inter alia to avoid any undesirable
coupling of the lateral surface of the fiber with the lateral walls
of the cavity 802. The end 805 of the fiber is connected to the
base of the cavity 802 by means of a transparent adhesive having a
refractive index similar to that of the fiber, for example of the
cyano-acrylate type. The base of the cavity is situated near the
focal point of the diopter so that the light issuing from the
diopter forms a substantially convergent beam which will form the
image of the end 805 on the entry face of the receiving diopter
forming the lens. This receiving diopter will focus the light thus
transmitted on the end of the transmitting fiber connected
thereto.
FIG. 9 shows part of the keyboard of FIG. 7 in the form of a
section taken along the channel 702 passing through the keys 5 and
8. The channel 702 is cut into a baseplate 901. This plate supports
a cover 902 drilled with holes where the keys 5 and 8 slide. A
layer of a flexible and elastic material, for example rubber,
covers the cover 902, closes all the holes and forms supporting
tubes 903 to the end of which are fixed the heads of the keys
widened out into a mushroom-like form. These supporting tubes 903
thus hold the keys in their upper position, allowing the light to
pass through (key 5 in the FIG.). The application of pressure to a
key (arrow N on the key 8 in the FIG.) depresses the key which
deforms the corresponding supporting tube, closing the channel 702
and the channel 701 which passes to this point and is perpendicular
thereto. When the key is released, it returns to its upper position
under the action of its supporting tube which forms a spring.
In order to ensure that the connection is broken when the hand set
is replaced, holes are drilled below certain keys and contain
shutters which, operated by the mechanical control ER, enable a
sufficient number of channels 701 and 702 to be closed. A shutter
of the type in question comprises for example a cylindrical base
904 surmounted by a crosshead 905 formed by two perpendicular
plates which each close one passage. In order to monitor the
continuity of the line, small holes may be drilled in these
crossheads, as in the FIG., or the crossheads may be made of a
slightly transparent material. It can be seen from FIG. 7 that it
is sufficient to have one shutter below the key 5 and one shutter
below the key F for the 16-key keyboard. For the 12-key keyboard,
only the shutter below the key 5 is necessary.
Accordingly, the telephone set thus described does not require
local power supply. It may comprise an input and/or an output for
the use of other apparatus, such as a teledata terminal for
example. In this case, where the terminal requires local power
supply, the input in question may be equipped with a light-emitting
diode for exciting the output fiber(s) through a multichannel
coupler. Although this diode will not be supplied with power from
the exchange, the telephone per se may always be used, even in the
event of local power failures, as required by regulations. The
available band width, even with any type of optical fiber, is
sufficient for receiving and/or transmitting television signals
converted to a frequency above the telephone band, which enables
videophone connections to be established under perfectly normal
economic conditions.
The optical power required for exciting the fiber FT is equal to
that required for attacking the microphone 111 and to that required
for the detector 115 to have a good signal to-noise ratio.
Taking the common value .eta.=0.4 A/W as the output of the
photovoltaic cell 108 and using a microphone current requiring 0.7
V for 600 ohms, the optical power required for the fiber 106 is
substantially 3 mW.
Given an optical power of 10 .mu.m at the input end of the detector
115 and losses in the dialling unit and in the microphone each
equal to 3 dB, with losses along the line FR equal to 10 dB, all
common values, the optical power required for the fiber 107 is
substantially 0.4 mW.
The coupler 105 currently reaches insertion losses of the order of
1 dB and the losses along the line FT will be of the same order as
the losses along the line FR, i.e. 10 dB. The optical power at the
input end of the coupler 105 will therefore amount substantially to
4.3 mW and at the output end of the source 104 to 43 mW.
A power of this order may be delivered for example by a
semiconductor laser having a wide emissive zone. At present a laser
of this type having an emissive zone of from 50 to 100 .mu.m emits
a power of approximately 1 mW per .mu.m of emissive zone width.
It has been seen that it would be possible to use a relatively
large optical fiber in excess of 100 .mu.m in diameter which will
therefore be readily excited by a laser of the type in question. At
the present time, a fiber of this type has an attenuation of
approximately 5 dB/km which enables the greatest number of local
connections to be established without a repeater.
* * * * *